where to put the probe ..... RE: [TCML] Grounding a Tesla Coil (Yes, Again)

[William Noble <william_b_noble@xxxxxxx>]

this poses an intersting, but not new, area of discussion.

 

several decades ago, I was faced with a similar problem on a large transport airplane - if you are looking for a ground loop, where do you attach the ground?  In the case of this (350,000 pound class) airplane, I was "measuring" 200V spikes from ground to ground - looking at a shield grounded near the middle of the airplane compared to a "ground" near the nose (and all of this across what is basically a huge aluminum "ground plane").  that was a surprise to me - to this day I don't know if what I was measuring was real, but some tweaking of the shield made the problem I was really looking for go away.

 

What I would do is establish a "master ground" node somewhere and reference to that, and run a shielded wire (with the shield also grounded at the master ground) from the master ground to the scope - then you can attach the probe to any other "ground" you want and you will get an indication of what's going on - I say indication because you still don't know for real what might be induced into your wires even with shielding

 


 
> Date: Mon, 10 May 2010 16:29:40 -0700
> From: jimlux@xxxxxxxxxxxxx
> To: tesla@xxxxxxxxxx
> Subject: Re: [TCML] Grounding a Tesla Coil (Yes, Again)
> 
> Gary Lau wrote:
> > Hi Jim,
> > 
> > On the issue of RF grounds in general, determining the relative
> > quality of one has always been nebulous. I'm pretty sure that the
> > consensus is that the ground quality has a minimal effect at best on
> > streamer length, so I don't think streamer length is a useful metric.
> > You wrote:
> >> Give it a shot and see if it works.
> > 
> > Short of just seeing if any appliance damage results, are you aware of
> > any means to quantify how well a given setup works, even relative to
> > an alternate setup? I once tried monitoring the AC mains through a
> > high-pass filter for transient spikes (assuming that a better ground
> > results in lower amplitude transients), but uncertainty of how to
> > ground the scope probe (and scope!) made me give up.
> > 
> 
> 
> You raise a very good point.
> 
> Looking for transients might work, except that where would you probe?
> And, even then, if you have a shunt type transient suppressor (like the
> MOVs found in all those plug strips) it might clip them (dying a little
> each time, until it catastrophically fails blowing the fuse in the plug
> strip if you're lucky)
> 
> 
> To a certain extent the empirical: "I did this and it didn't kill the
> expensive electronics of my spouse/significant other/parent/children" is
> what we've all done in the past.
> 
> 
> OK, but recognizing that we need some quantitative answers. What would
> be a good experiment?
> 
> There are two aspects to the transients from TCs.. the radiated field
> (mostly magnetic near field from the sparks discharging the topload) and
> conducted (via the power cord, presumably). I'm going to assume that
> you can kill any differential mode power cord signals with a good line
> filter.
> 
> So, we're looking at common mode signals propagated down the power cord
> (treating the entire cord as a unit) and the radiated fields from the
> discharge.
> 
> 
> Could we set up a "victim loop" at some distance to represent a receiver
> of the radiated fields?
> 
> And, for the common mode current through the power cord: it couples to
> the "greenwire ground" in your house and sets up a circuit.. from TC
> through cord to house wiring to capacitive coupling to topload. How
> about measuring the RF current in the cord as a whole, using a suitable
> transformer.
> 
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
 		 	   		  _______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla